Mechanical and microstructural properties evaluation of AISI4130 steel after backward flow forming process

Flow forming is one of the advanced methods for producing low thickness cylindrical parts. The dimensional accuracy of pipes produced by the flow forming method is much higher than other methods and this method is widely used in the aerospace industry. In this research, the effect of number flow forming passes has been investigated on the mechanical properties and microstructure of AISI4130 steel. Three stages of thickness reduction have been successfully completed and in the fourth stage, the tube was fractured. In the first stage of this pass, the desired steel thickness has changed from 14.2 mm to 9.3 mm. In the second stage, the thickness reached 2.6 mm, in the third stage to a thickness of 2.3 mm and in the fourth stage by reaching 1.8 mm thick, there has been a tear in the pipe. During the flow forming process, the maximum amount of 84.5% thickness reduction can be achieved. To achieve a higher percentage of thickness reduction, it is necessary to re-anneal the flow formed sample. To investigate the tensile properties, tensile tests have been done through both longitudinal and circumferential directions. According to the results, it was found that the flow forming operation on this steel has increased the hardness and yield, and ultimate strength of the material at every stage. Also, the hard work done at every stage on this steel by maintaining the ferritic pearlite-ferritic structure has caused finer grain structure and elongation of the grains.